1. Field of the Invention
The invention relates to systems for counting and timing swim laps, and to methods for event detection from noisy source data.
2. Description of Related Art
Swimming as a sport dates to the ancient Greeks and has been a competitive sport in every modern Olympics. A number of high-profile national and Olympic competitors in recent years have only made it more popular. In competitive swimming events, the swimmers swim one or more lengths of a pool, each two lengths equaling one lap, turning at each end of the pool to begin the next length. For serious and competitive swimmers, counting and timing these laps is important in measuring individual progress toward goals, as well as in determining the winner of any particular race. For recreational swimmers and those who only swim for health, the distance covered is often of primary importance, with distance measured by the number of laps. Lap counting without external aids occupies a swimmer's thoughts and is tedious and unreliable, aside from which it can be very difficult to judge one's progress and observe distance and time during a swim, especially since most devices used to do so are out of the water or are attached to the body.
In officially-sanctioned competitive races, touch pads are usually provided at the ends of the pool, and as the swimmers turn to begin a new lap, they toggle the pad, which provides both verification that the lap has been properly completed and an accurate time for the lap. As accurate and accepted as these systems are, they are typically only available to competitors swimming in appropriately-equipped pools, and can cost many thousands of dollars. They are not designed for use by individuals, but rather for teams supervised by coaches. These types of devices are rarely used for individual workouts.
Timing and counting systems for individual swimmers and pools not equipped with touchpads are available. U.S. Pat. No. 5,125,010, for example, is representative of a class of devices that use a poolside unit and a wearable transmitter to time the swimmer and count laps. The poolside unit communicates with the transmitter, which is attached to the swimmer. In this patent, the two devices communicate with each other using radio frequencies, although other examples of lap counters, like the system disclosed in U.S. Pat. No. 4,823,367, attach a passive marker to the swimmer and reflect energy, like infrared beams, off of it. These types of systems continue to be made and improved; U.S. Pat. No. 6,870,466 discloses a more recent example of this type of system. A variation on this is disclosed in U.S. Patent Application Publication No. 2014/0200116, which uses a machine vision system coupled with an optical marker mounted near the swimmer's hips. All of the above-described patents are incorporated by reference in their entireties.
Systems that use a fixed unit and a portable transmitter, reflective marker, or counting unit on the swimmer have significant drawbacks. For example, the portable transmitter or marker may be uncomfortable to wear, or may cause significant drag or turbulence around the swimmer, thereby affecting biomechanics and performance. In addition, the motion of the swimmer and the environment of the water—with turbulence and thousands of disruptive bubbles—can potentially cause unreliable communications. Certain types of communications are particularly susceptible to this kind of disruption. For example, absorption of infrared light is stronger in water than in air, and laser light is particularly susceptible to disruption by bubbles.